Rio+20 to redefine sustainable development for megacities

One of the most striking changes at Rio+20, compared to the original 1992 Earth Summit, is the extensive discussion of population issues. In part, this is driven by the fact that many developing countries, including the BRICs, are seeking to redefine what sustainability means with their generally rapid annual growth rates, and high population growth which is estimated to see world population rise from around 7bn today, to between 8bn and 11bn by 2050.

This reminds us of the massive challenges, especially in the developing world, created by an ever-increasing number of humans on the planet.

Growing populations are also driving another mega trend - urbanisation through migration. In 1800, less than 3 percent of the population lived in cities, yet by the end of 2008, this had risen to more than 50 percent, and there were 26 megacities (cities of 10n or more inhabitants), including Rio itself.

Despite the economic success of megacities, governments at every level are preparing for the growing risks that these massive urban centres pose. It is therefore fitting that one of the focal points of Rio+20 is laying the foundations for a more sustainable development model for megacities.

Key questions to be addressed include whether it will be possible to continually meet the everyday needs of food, water and health, and also deal with the growing vulnerability of megacities to environmental stresses exacerbated by the effects of climate change?

There is already cause for some alarm. For instance, the 2003 heat-wave in Paris was so devastating because both the public and authorities were unprepared for dealing with such extreme weather conditions, which were exacerbated by building practices, especially the lack of air-conditioning. Moreover, the tsunami in Japan last year forced Tokyo to re-consider its approach to nuclear power and to protecting its cities.

During the 21st century, megacities across the world will continue to grow, as will other large urban conglomerations which have megacity features. Energy demands will thus increase as supplies of food, water and resources for industries and infrastructure require energy for transportation.

The associated increased carbon emissions are contributing to global warming and pose their own climate risks. In China, where people are being subsidised to move from the countryside, cities have grown by a factor of two in only five years. The local urban ‘heat island’ effect means temperatures are increasing about three times faster than the rate of temperature rise over global and national land areas.

The main risk for riverine megacities on coastal plains is their increasing vulnerability to rising sea levels and river flooding. There will be further episodes such as the one in New Orleans seven years ago when it was hit by Hurricane Katrina, without adequate protection and flood warning systems.

In at-risk countries, such as the Netherlands, researchers are preparing for these type of problems. For instance, Delft University’s Hydraulic Engineering Department has been developing a state of the art early warning and monitoring system, including the effects of subsidence, to protect coastal communities.